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Posted: 9/3/2011 10:45:00 AM EDT
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What's the story on the rubber donut that fits over the AR extractor spring? Is it newly Milspec or something? I see it included in upgrade kits, but just bought three PSA bolts that had the black insert but no donut. I also see extractor springs being offered with the black insert, but again, with no donut. Then again I see recommendations that it always be used. So what's the real story on this little gizzy - nice to have, need to have, must have, what?
MM |
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Short barrels have shorter dwell times which can cause the brass to have not relaxed from the chamber wall when extraction starts. This was causing occasional fte on M4 carbines and commando models, so colt replaced the blue insert with the black.
Steel cases and rough chambers can be even harder to extract, leading to the commercial development of the rubber rings to add even more tension to the extractor. You can pay $13 for a name-brand D-fender insert or $.60 for a #60 viton oring at the hardware store. The rings are not milspec, but the black inserts are. |
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Quoted:
OK guys, thanks very much. That about says it all. I'm putting together a small parts order and the donuts are only fifty cents, so I'll give them a try. Thanks again. MM Before I'd put a donut or o-ring in my rifle I'd use a BCM extractor spring, or a gold spring from Colt. |
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I needed to use the ring on my AR Pistol that had the 7" barrel.It would not hold the case on extraction.
My 20" rifles have zero problems without them. My 16" rifles don't need them either. My Carbines and my SBR have them. Sometimes the SBR would slip a case off the extractor and double-feed,so it does seem to depend on how hard the bolt is working.Short barrels are very harsh on extraction,that is a known fact. Long barrels don't need them,but short barrels do. |
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I use BCM extractor upgrade kit which consists of a 5 coil extractor spring (chrome silicon, heat treated, stress relieved, shot peened), mil-spec Crane Ind. O-ring and black extractor insert on my 3 carbine gas system.
When I first installed the kit I didn't use the O-ring because the extractor spring is so strong, so I break it in for around 600 to 1K rounds then after that I installed the O-ring. For my midlength and rifle gas system I only use the black extractor insert and O-ring, it doesn't need the extra strength extractor spring. I also buy some mil-spec Crane O-ring from ADCO. All my AR works pretty good without any problems, I'm very satisfied with my upgrades. I would recommend to get the 3 pack kit and keep some spare kits for future use. BCM Extractor Spring Uprade Kit - link |
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